In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of a Device to Device (D2D) proximity service is discussed as a new function in Release 12 and later (see Non Patent Document 1).
The D2D proximity service (D2D ProSe) is a service enabling direct Device-to-Device communication within a synchronization cluster including a plurality of synchronized user terminals. The D2D proximity service includes a D2D discovery procedure (Discovery) in which a proximal terminal is discovered and D2D communication (Communication) that is direct Device-to-Device communication.